Film with high impact strength

ABSTRACT

A film with a broad molecular weight distribution, excellent impact strength and a high dart drop value or moderate dart drop value accompanied by good optical property consisting of a bimodal terpolymer comprising a low molecular weight homopolymer of ethylene and a high molecular weight terpolymer of ethylene, 1-butene and a C6 to C12 alpha-olefin, or a bimodal terpolymer comprising a low mo-lecular weight polymer which is a binary copolymer of ethylene and a C4 to C12 alpha-olefin and a high molecular weight polymer which is either a binary copolymer of ethylene and 1-butene, if the low molecular weight polymer is a binary co-polymer of ethylene and a C6 to C12 alpha-olefin, or a terpolymer of ethylene, 1-butene and a C6 to C12 alpha-olefin.

The present invention relates to a film with good mechanical properties,in particular to a film of a bimodal terpolymer with a good impactstrength.

Bimodal ethylene polymers are well known and can be used for manyapplications as pressure pipes, cable jacketing, wire coating, pipecoating, blow moulding and films.

Such polymers consist in general of two polymers one having a relativelyhigh molecular weight and one having a relatively low molecular weight.The properties of these polymers are a good tensile strength, a highultimate elongation, a good puncture resistance and a good impactstrength.

Document EP-0 369 436 A2 is related to a process for the in-situblending of polymers comprising continuously contacting underpolymerisation conditions, a mixture of ethylene and at least oneα-olefin having at least three carbon atoms. The final polymer comprisesa low melt index copolymer and a high melt index copolymer whereby bothcopolymers consist of ethylene and an α-olefin. The document is relatedto a process and does not show any specific reasons why the polymerswould be useful in manufacturing films.

Document EP-0 435 624 A1 provides a low density polyethylene having arelatively broad molecular weight distribution and therefore goodprocessability at high molecular weights. The polymer used as a film isproduced by blending the first polymer component of high molecularweight with a second polymer component of low molecular weight, wherebyboth polymer components having substantially the same melt indexcorrected density or a dissimilar corrected density.

Document EP-0 691 367 B1 is related to an extruded film of ethylenecopolymers prepared in a series of polymerisation reactors, whereby ahigh molecular weight fraction consists of a copolymer of ethylene andα-olefin comonomer(s) having 5 to 12 carbon atoms and a low molecularweight fraction consists of a copolymer of ethylene, 1-butene andoptionally an α-olefin comonomer(s) having 3 to 12 carbon atoms.

Document WO-97/49476 is related to cable constructions, particularlyjacketing for telecommunication cables. Best mechanical results for suchcable jackets can be obtained when 1-butene is used as a comonomer inthe low molecular weight fraction and 1-hexene in the high molecularfraction or vice versa. The prior art document WO-97/49476 does notdisclose films and properties that are important in the production.

An improvement of impact strength is still desirable.

It is therefore an object of the present invention to provide a filmwith a high impact strength, especially a film with a high dart dropvalue, or alternatively a film with moderate dart drop value andsimultaneously having good optical properties.

The present invention is based on the finding that these objects can besolved by a film of a bimodal terpolymer comprising a low molecularweight polymer which contains at least ethylene and a high molecularweight polymer which is a binary copolymer or a terpolymer depending onthe composition of the low molecular weight polymer.

More precisely, the object is solved by a film which consists of eithera bimodal terpolymer comprising

-   -   a) a low molecular weight homopolymer of ethylene and    -   b) a high molecular weight terpolymer of ethylene, 1-butene and        a C₆ to C₁₂ α-olefin,        or a bimodal terpolymer comprising    -   a) a low molecular weight polymer which is a binary copolymer of        ethylene and a C₄ to C₁₂ α-olefin and    -   b) a high molecular weight polymer which is either a binary        copolymer of ethylene and 1-butene, if the low molecular weight        polymer of a) is a binary copolymer of ethylene and a C₆ to C₁₂        α-olefin, or a terpolymer of ethylene, 1-butene and a C₆ to C₁₂        α-olefin.

In a first and second embodiment the present invention provides a filmof a bimodal, high molecular weight terpolymer with at least a broadmolecular weight distribution and excellent impact strength, especiallya film with at least a high dart drop value, and in a third embodimentthe present invention provides a film of a bimodal, medium molecularweight terpolymer with a relatively narrow molecular weight distributionand moderate dart drop value accompanied by good optical property.

Furthermore, the present invention provides a process for producing thefilm of a bimodal terpolymer with the above mentioned properties.

In the following all three embodiments will be explained in more detail.

The film of the first embodiment is a bimodal, high molecular weightterpolymer with a very broad molecular weight distribution whereby itsremarkable feature is the excellent impact strength, especially a filmwith a very high dart drop value. A film with such properties ischaracterized in that the film consists of either a bimodal terpolymercomprising

-   -   a) a low molecular weight homopolymer of ethylene and    -   b) a high molecular weight terpolymer of ethylene, 1-butene and        a C₆ to C₁₂ α-olefin,        or a bimodal terpolymer comprising    -   a) a low molecular weight polymer which is a binary copolymer of        ethylene and a C₄ to C₁₂ α-olefin and    -   b) a high molecular weight polymer which is either a binary        copolymer of ethylene and 1-butene, if the low molecular weight        polymer of a) is a binary copolymer of ethylene and a C₆ to C₁₂        α-olefin, or a terpolymer of ethylene, 1-butene and a C₆ to C₁₂        α-olefin.

The expression of modality of a polymer refers to the form of itsmolecular weight distribution (MWD) curve, i.e. the appearance of thegraph of the polymer weight fraction as a function of its molecularweight. If the polymer is produced in a sequential step process i.e. byutilizing reactors coupled in series and using different conditions. ineach reactor, the different polymer fraction produced in the differentreactors will each have their own molecular weight distribution whichmay considerably differ from each another.

The molecular weight distribution curve of the resulting final polymercan be looked at as the superposition of the molecular weightdistribution curve of the polymer fractions which will accordingly showtwo or more distinct maxima or at least be distinctly broadened comparedwith the curves of the individual fractions. A polymer showing such amolecular weight distribution curve is called bimodal or multimodal,respectively.

Multimodal, especially bimodal, polymers can be produced according toseveral processes which are described e.g. in EP-0 517 868 B1 orWO-A-96/18662.

The multimodal polyethylene preferably is produced in a multi-stageprocess in a multi-step reaction sequence such as described in EP-0 517868 B1 and WO-A-96/18662. The contents of these documents are includedherein by reference.

In this process, in a first step ethylene is polymerized in a loopreactor in the liquid phase of an inert low boiling hydrocarbon medium.Then the reaction mixture is discharged from the loop reactor and atleast the inert hydrocarbon medium is removed from the reaction mixtureand the polymers transferred into one or more gas phase reactors wherethe polymerisation is continued in the presence of gaseous ethylene. Themultimodal polymer produced according to this process has a superiorhomogenity with respect to the distribution of the different polymerfractions which cannot be obtained e.g. by a polymer mix.

The catalyst for the production of the ethylene polymer may be e.g. achromium, a Ziegler-Natta-type or a single-site catalyst.

Preferably, a Ziegler-Natta catalyst, like one of those disclosed inEP-A-0 688 794 and EP-A-0 949 274 or a single-site catalyst like one ofthose disclosed in WO-A-97/28170 is used.

Multimodal polymers, in particular ethylene polymers, show superiormechanical properties such as low shrinkage, low abrasion, hard surfaceand good barrier properties accompanied by a good processability.

The bimodal terpolymer according to the first embodiment comprises a lowmolecular weight fraction (LMW) of a homopolymer of ethylene or a binarycopolymer of ethylene and a C₄ to C₁₂ α-olefin and a high molecularweight fraction (HMW) of a binary copolymer of ethylene and 1-butene ifthe low molecular weight polymer of a) is a binary copolymer of ethyleneand a C₆ to C₁₂ α-olefin, or a terpolymer of ethylene, 1-butene and a C₆to C₁₂ α-olefin.

The expression “homopolymer of ethylene” used herein refers to apolyethylene that consists substantially, i.e. to at least 98% byweight, preferably at least 99% by weight, more preferably at least99.5% by weight, most preferably at least 99.8% by weight of ethylene.

The impact strength characterizes the material behaviour and a highspeed loading (impact). Pendulum and falling weight type testers areapplied here. Specimen can be either plaques, notched or unnotched barsor parts of finished products. There are several impact methods like“Charpy impact test”, “Izod impact test”, “tensile impact test”,“instrumented puncture test” and the “dart drop test”. Generally, animpact test shows the energy which is needed to break or puncturespecimen under specified conditions. By the dart drop test the dart dropvalue is determined to verify the impact strength of a film. Afree-falling dart of specific weight and geometry is therefore from aspecified height dropped onto a film. The weight at which 50% of thefilm samples break is reported as the dart drop value. All dart dropvalues are measured by method ISO 7765-1.

The film according to the first embodiment if extruded on a Collin filmline into a thickness of 25 μm with a die diameter of 30 mm, a die gapof 0.75 mm, a BUR (blow-up ratio) of 3.2 and a frost line height of 160mm, has a dart drop value preferably of at least. 1,400 g, morepreferably of at least 1,500 g and most preferably of at least 1,700 g.

The bimodal terpolymer composition comprises, as stated above, a lowmolecular weight copolymer fraction and a high molecular weightcopolymer fraction. The low molecular copolymer fraction contains,provided that a binary copolymer is used, a C₄ to C₁₂ α-olefin.Preferably, the C₄ to C₁₂ α-olefin of the low molecular weight copolymerfraction is selected from the group of 1-butene, 1-hexene,4-methyl-1-pentene, 1-octene and 1-decene. The C₆ to C₁₂ α-olefin of thehigh molecular weight copolymer fraction is preferably selected from thegroup of 1-hexene, 4-methyl-1-pentene, 1-octene and 1-decene.

The weight average molecular weight of the bimodal terpolymer ispreferably between 190,000 to 400,000 g/mol, more preferably between200,000 to 300,000 g/mol. The low molecular weight polymer fraction hasa weight average molecular weight preferably of 4,500 to 55,000 g/mol,more preferably of 5,000 to 50,000 g/mol and the high molecular weightpolymer has a weight average molecular weight preferably of 450,000 to1,000,000 g/mol, more preferably of 500,000 to 1,000,000 g/mol.

The molecular weight distribution of the polymer is furthercharacterized by the way of its melt flow rate (MFR) according to ISO1133 at 190° C. The melt flow rate is preliminary depending on the meanmolecular weight. This is, because long, well-packed molecules give thematerial a lower flow tendency than short, less-packed molecules.

An increase in molecular weight means a decrease in MFR value. The meltflow rate is measured in g/10 min of the polymer discharge under aspecified temperature and pressure condition and is a measure of theviscosity of the polymer, which in turn for each type of polymer ismainly influenced by its molecular weight distribution, but also by itsdegree of branching etc. The melt flow rate measured under a load 2.16kg (ISO 1133) is denoted as MFR₂. In turn, the melt flow rate measuredwith 21.6 kg is denoted as MFR₂₁.

The final bimodal terpolymer has a melt flow rate MFR₂₁ preferably of 7to 40 g/10 min, more preferably of 15 to 30 g/10 min. The low molecularweight polymer has a melt index MFR₂ preferably of 200 to 800 g/10 min,more preferably of 300 to 600 g/10 min.

The melt flow rate and the density of the material are decisive forstrength properties, while the density only is decisive for the meltingpoint, surface hardness, permeability and water absorption.

The density of the final bimodal terpolymer is preferably of 910 to 950kg/M³, more preferably of 915 to 940 kg/m³. The density of the lowmolecular weight polymer is preferably of 940 to 980 kg/m³, morepreferably of 945 to 975 kg/M³.

The film of the bimodal terpolymer according to the present invention,consists preferably in 30 to 60%, more preferably 35 to 50% and mostpreferably 38 to 45% by weight of low molecular weight copolymer withregard to the total composition.

The overall comonomer content in the total polymer is 1 to 7% by mol,preferably 2 to 6% by mol and in the low molecular weight polymer is thecomonomer content 0 to 2.5% by mol, preferably 0 to 2% by mol. In thehigh molecular weight polymer is the comonomer content 2.5 to 11% bymol, preferably 3 to 10% by mol.

Further, the molecular weight of the high molecular weight copolymerfraction should be such that when the low molecular weight copolymerfraction has the melt index and density specified above, the finalbimodal terpolymer has the melt index and density as discussed above.

In the following some preferred compositions are explicitly described.

It is preferred that the bimodal terpolymer has a melt flow rate MFR₂₁of about 10 to 40 g/10 min and a density of 918 to 928 kg/m³.

According to another preferred product, the bimodal terpolymer has amelt flow rate MFR₂₁ of about 7 to 30 g/10 min and a density of 930 to940 kg/m³.

According to one more preferred product, the bimodal terpolymer has amelt flow rate MFR₂₁ of about 7 to 20 g/10 min and a density of 940 to950 kg/m³.

Preferably, the bimodal terpolymer comprises a low molecular weightcopolymer fraction consisting in a binary copolymer of ethylene and a C₆to C₁₂ α-olefin and a high molecular weight copolymer fractionconsisting in a binary copolymer of ethylene and 1-butene. The melt flowrate MFR₂₁ of the final bimodal terpolymer is of about 10 to 40 g/10 minand the density amounts to 918 to 928 kg/m³, whereby the low molecularweight copolymer fraction has a melt flow rate MFR₂ of 200 to 500 g/10min and a density of 945 to 955 kg/m³. The amount of the low molecularweight copolymer fraction is 38 to 43% of the total composition and theamount of high molecular weight copolymer is 57 to 62% of the totalcomposition. A bimodal terpolymer with properties as stated in thisparagraph has, as a film, a dart drop value preferably of at least 1400g, more preferably of at least 1500 g, if the film is extruded on aCollin film line into a thickness of 25 μm, with a die diameter of 30mm, a die gap of 0.75 mm, a BUR (blow-up ratio) of 3.2 and a frost lineheight of 160 mm.

In another preferred composition the bimodal terpolymer comprises a lowmolecular weight copolymer fraction consisting in a binary copolymer ofethylene and a C₆ to C₁₂ α-olefin and a high molecular weight copolymerfraction consisting in a binary copolymer of ethylene and 1-butene. Themelt flow rate MFR₂₁ of the final bimodal terpolymer is about 7 to 30g/10 min and the density amounts to 930 to 940 kg/m³, whereby the lowmolecular weight copolymer fraction has a melt flow rate MFR₂ of 200 to800 g/10 min and a density of 955 to 965 kg/m³. The amount of the lowmolecular weight copolymer fraction is 38 to 43% of the totalcomposition and the amount of high molecular weight copolymer fractionis 57 to 62% of the total composition.

In still another preferred composition the bimodal terpolymer comprisesa low molecular weight copolymer fraction consisting in a homopolymer ofethylene or a binary copolymer of ethylene and 1-butene and a highmolecular weight copolymer fraction consisting in a terpolymer ofethylene, 1-butene and a C₆ to C₁₂ α-olefin. The melt flow rate MFR₂₁ ofthe final bimodal terpolymer is about 7 to 30 g/10 min and the densityamounts to 930 to 940 kg/m³, whereby the low molecular weight copolymerfraction has a melt flow rate MFR₂ of 200 to 800 g/10 min and a densityof 955 to 975 kg/m³. The amount of the low molecular weight copolymerfraction is 38 to 43% of the total composition and the amount of highmolecular weight copolymer fraction is 57 to 62% of the totalcomposition.

The film of the second embodiment is a bimodal, high molecularterpolymer with a broad molecular weight distribution whereby itsremarkable feature is the excellent impact strength, especially a filmwith a high dart drop value. Furthermore, the film of the secondembodiment has higher stiffness and moisture properties than those ofthe first and third embodiment, due to the higher density of the film. Afilm with such properties is characterized in that the film consists ofa bimodal terpolymer comprising

-   -   a) a low molecular weight homopolymer of ethylene and    -   b) a high molecular weight terpolymer of ethylene, 1-butene and        a C₆ to C₁₂ α-olefin,

The bimodal terpolymer of the second embodiment can be produced in thesame manner as already described in the first embodiment. This relatesalso to the catalyst types which can be used.

The expression “homopolymer of ethylene” used herein refers to apolyethylene that consists substantially, i.e. to at least 98% byweight, preferably at least 99% by weight, more preferably at least99.5% by weight, most preferably at least 99.8% by weight of ethylene.

Preferably, the C₆ to C₁₂ α-olefin is selected from the group of1-hexene, 4-methyl-1-pentene, 1-octene and 1-decene.

The film according to the second embodiment if extruded on a Collin filmline into a thickness of 25 μm, with a die diameter of 30 mm, a die gapof 0.75 mm, a BUR (blow-up ratio) of 3.2 and a frost line height of 160mm, has a dart-drop value of at least 180 g, preferably of at least 200g.

The weight average molecular weight of the bimodal terpolymer is between240,000 to 500,000 g/mol, preferably 250,000 to 400,000 g/mol. The lowmolecular weight polymer fraction has a weight average molecular weightpreferably of 4,500 to 55,000 g/mol, more preferably of 5,000 to 50,000g/mol and the high molecular weight polymer has a weight averagemolecular weight preferably of 450,000 to 1,000,000 g/mol, morepreferably of 500,000 to 1,000,000 g/mol.

The final bimodal terpolymer has a melt flow rate MFR₂₁ preferably of 2to 25 g/10 min, more preferably of 3 to 20 g/10 min. The low molecularweight polymer has a melt index MFR₂ preferably of 300 to 1,200 g/10min, more preferably of 300 to 600 g/10 min.

The density of the final bimodal terpolymer is preferably of 935 to 970kg/m³, more preferably of 940 to 965 kg/m³. The density of the lowmolecular weight polymer is preferably of 970 to 980 kg/m³, morepreferably of 972 to 978 kg/m³, most preferably 975 kg/m³.

The film of the bimodal terpolymer according to the present invention,consists preferably in 30 to 60%, more preferably 35 to 50% and mostpreferably 38 to 45% by weight of low molecular weight copolymer withregard to the total composition.

The overall comonomer content in the total polymer is 0.5 to 2.5% bymol, preferably 0.5 to 2.5% by mol and in the high molecular weightpolymer is the comonomer content 0.5 to 3.5% by mol, preferably 0.7 to3.0% by mol.

Further, the molecular weight of the high molecular weight copolymerfraction should be such that when the low molecular weight copolymerfraction has the melt index and density specified above, the finalbimodal terpolymer has the melt index and density as discussed above.

It is preferred that the bimodal terpolymer has a melt flow rate MFR₂₁of about 3 to 20 g/10 min and a density of 955 to 965 kg/m³.

In a preferred composition the bimodal terpolymer comprises a lowmolecular weight copolymer fraction consisting of a homopolymer ofethylene and a high molecular weight copolymer fraction consisting in aterpolymer of ethylene, 1-butene and a C₆ to C₁₂ α-olefin. The melt flowrate MFR₂₁ of the final bimodal terpolymer is about 3 to 20 g/10 min andthe density amounts to 940 to 950 kg/m³, whereby the low molecularweight copolymer fraction has a melt flow rate MFR₂ of 300 to 1200 g/10min. The amount of the low molecular weight copolymer fraction is 38 to43% of the total composition and the amount of the high molecular weightcopolymer fraction is 55 to 62% of the total composition. A bimodalterpolymer with properties as stated in this paragraph has, as a film, adart drop value preferably of at least 190 g, more preferably of atleast 200 g, if the film is extruded on a Collin film line into athickness of 25 μm, with a die diameter of 30 mm, a die gap of 0.75 mm,a BUR (blow-up ratio) of 3.2.

In one more preferred composition the bimodal terpolymer comprises a lowmolecular weight copolymer fraction consisting in a homopolymer ofethylene and a high molecular weight copolymer fraction consisting in aterpolymer of ethylene, 1-butene and a C₆ to C₁₂ α-olefin. The melt flowrate MFR₂₁ of the final bimodal terpolymer is about 3 to 20 g/10 min andthe density amounts to 955 to 965 kg/m³, whereby the low molecularweight ethylene polymer fraction has a melt flow rate MFR₂ of 300 to1200 g/10 min. The amount of the low molecular weight copolymer fractionis 38 to 43% of the total composition and the amount of high molecularweight copolymer fraction is 57 to 62% of the total composition.

The film of the third embodiment consists in a medium molecular weightpolymer having a relative narrow molecular weight distribution, wherebythe film has moderate dart drop value accompanied by good opticalproperties. These films are mainly used in packaging where the strengthis not a decisive factor but transparency is important.

The film according to the third embodiment consists of a bimodalterpolymer comprising

-   -   a) a low molecular weight polymer which is a binary copolymer of        ethylene and a C₄ to C₁₂ α-olefin and    -   b) a high molecular weight polymer which is either a binary        copolymer of ethylene and 1-butene, if the low molecular weight        polymer of a) is a binary copolymer of ethylene and a C₆ to C₁₂        α-olefin, or a terpolymer of ethylene, 1-butene and a C₆ to C₁₂        α-olefin.

The bimodal terpolymer of the third embodiment can be produced in thesame manner as already described in the first embodiment. This relatesalso to the catalyst types which can be used.

The bimodal terpolymer composition comprises as stated above a lowmolecular copolymer fraction and a high molecular copolymer fraction.The low molecular copolymer fraction contains a C₄ to C₁₂ α-olefin,which is preferably selected from the group of 1-butene, 1-hexene,4-methyl-1-pentene, 1-octene and 1-decene. The C₆ to C₁₂ α-olefin of thehigh molecular weight copolymer fraction is preferably selected from thegroup of 1-hexene, 4-methyl-1-pentene, 1-octene and 1-decene.

The film according to the third embodiment if extruded on a Collin filmline into a thickness of 25 μm, with a die diameter of 60 mm, die gap of1.5 mm, BUR (blow-up ratio) of 2 and a frost line height of 120 mm, hasa dart-drop value preferably over 50 g, more preferably over 60 g andmost preferably over 63 g.

Further, the film with a dart-drop value as stated in the aboveparagraph has preferably haze value equal or less than 20, morepreferably equal or less than 16, and has preferably a gloss value of atleast 60, more preferably of at least 73.

The weight average molecular weight of the bimodal terpolymer is between110,000 to 210,000 g/mol, preferably 120,000 to 200,000 g/mol. The lowmolecular weight polymer fraction has a weight average molecular weightpreferably of 25,000 to 110,000 g/mol, more preferably of 30,000 to100,000 g/mol and the high molecular weight polymer has a weight averagemolecular weight preferably of 100,000 to 400,000 g/mol, more preferablyof 150,000 to 370,000 g/mol.

The final bimodal terpolymer has a melt flow rate MFR₂₁ preferably of 15to 80 g/10 min, more preferably of 20 to 70 g/10 min. The low molecularweight polymer has a melt index MFR₂ preferably of 1 to 50 g/10 min,more preferably of 2 to 20 g/10 min.

The density of the final bimodal terpolymer is preferably of 900 to 935kg/m³, more preferably of 915 to 930 kg/m³ and in particular 920 to 925kg/m³. The density of the low molecular weight polymer is preferably of925 to 950 kg/m³, more preferably of 930 to 940 kg/m³.

The film of the bimodal terpolymer according to the third embodiment,consists preferably in 30 to 60%, more preferably 35 to 50% and mostpreferably 38 to 45% by weight of low molecular weight copolymer withregard to the total composition.

The overall comonomer content in the total polymer is 1 to 7% by mol,preferably 2 to 6% by mol and in the low molecular weight polymer is thecomonomer content 0.5 to 3.5% by mol, preferably 1 to 3% by mol. In thehigh molecular weight polymer is the comonomer content 3.5 to 10.5% bymol, preferably 4 to 10% by mol.

Further, the molecular weight of the high molecular weight copolymerfraction should be such that when the low molecular weight copolymerfraction has the melt index and density specified above, the finalbimodal terpolymer has the melt index and density as discussed above.

In a further preferred composition the bimodal terpolymer comprises alow molecular weight copolymer fraction consisting in a binary copolymerof ethylene and 1-butene and a high molecular weight copolymer fractionconsisting in a terpolymer of ethylene, 1-butene and a C₆ to C₁₂α-olefin. The melt flow rate MFR₂ of the final bimodal terpolymer isabout 0.5 to 2 g/10 min and the density amounts to 918 to 928 kg/m³,whereby the low molecular weight copolymer fraction has a melt flow rateMFR₂ of 2 to 20 g/10 min and a density of 930 to 950 kg/m³. The amountof the low molecular weight copolymer fraction is 38 to 43% of the totalcomposition and the amount of the high molecular weight copolymerfraction is 57 to 62% of the total composition.

In addition to the bimodal terpolymer of all three described embodimentsthe composition may also contain antioxidants, process stabilizers,pigments and other additives known in the art.

Examples of stabilizers are hindered phenols, hindered amines,phosphates, phosphites and phosphonites.

Examples of pigments are carbon black, ultra marine blue and titaniumdioxide. Examples of other additives are e.g. clay, talc, calciumcarbonate, calcium stearate, zinc stearate and antistatic additives likethose sold under trademark name “Lanirostat”.

The bimodal terpolymers according to all three embodiments may beproduced using any known methods where ethylene is polymerized in thepresence of a catalyst, preferably a Ziegler-Natta or single-sitecatalyst. They may be produced by a solution polymerization process, aslurry polymerization process or a gas polymerization process.

Preferably, the bimodal terpolymer is produced in a multi stage processlike those disclosed in EP-B-0 517 868 and WO-A-96/18662. Preferably,the polymerization takes place either in the presence of a Ziegler-Nattacatalyst like one of those disclosed in EP-A-0 688 794 and EP-A-0 949274, or in the presence of a single-site catalyst like one disclosed inWO-A-97/28170.

Preferably, the low molecular weight copolymer fraction is produced inone stage of a multi stage polymerization process and the high molecularweight copolymer fraction in another stage of the process. Morepreferably, the low molecular weight copolymer fraction is produced in acontinuously operating loop reactor where ethylene is polymerized in thepresence of a polymerization catalyst as stated above and chain transferagent such as hydrogen. The diluent is an inert aliphatic hydrocarbon,preferably isobutane or propane. A C₄ to C₁₂ α-olefin comonomer ispreferably added to control the density of the low molecular weightcopolymer fraction.

Preferably, the hydrogen concentration is selected so that the lowmolecular weight copolymer fraction has the desired melt flow rate. Morepreferably, the molar ratio of hydrogen to ethylene is between 0.1 and1.0 mol/mol, most preferably, between 0.2 and 0.8 mol/mol.

In the case the target density of the low molecular weight copolymerfraction exceeds 955 kg/m³, it is advantageous to operate the loopreactor using propane diluent in so called supercritical conditionswhere the operating temperature exceeds the critical temperature of thereaction mixture and the operating pressure exceeds the criticalpressure of the reaction mixture. A preferred range of temperature isthen from 90 to 110° C. and the range of pressures is from 50 to 80 bar.

The slurry is intermittently or continuously removed from the loopreactor and transferred to a separation unit where the hydrocarbonsincluding the eventually used C₄ to C₁₂ α-olefin comonomer andespecially the chain transfer agents are separated from the polymer. Thepolymer containing the active catalyst is introduced into a gas phasereactor where the polymerization proceeds in the presence of additionalethylene, 1-butene and optional C₄ to C₁₂ α-olefin comonomer andoptionally chain transfer agent to produce the high molecular weightcopolymer fraction. The polymer is intermittently or continuouslywithdrawn from the gas phase reactor and the remaining hydrocarbons areseparated from the polymer. The polymer collected from the gas phasereactor is the bimodal terpolymer.

The conditions in the gas phase reactor are selected so that theethylene polymer has the desired properties. Preferably, the temperaturein the reactor is between 70 and 100° C. and the pressure is between 10to 40 bar. The hydrogen to ethylene molar ratio ranges from preferably0.0001 to 0.02 mol/mol, more preferably 0.001 to 0.1 mol/mol and theα-olefin comonomer to ethylene molar ratio ranges from preferably 0.03to 0.7 mol/mol, more preferably 0.04 to 0.6 mol/mol and most preferably0.05 to 0.5 mol/mol.

In order to further illustrate the present invention preferredembodiments are given in the following by way of examples.

EXAMPLES

MFR

MFR was measured according to ISO 1133 at 190° C. The load has beenindicated as a subscript, i.e. MFR₂ denotes the measurement has beencarried out under a load of 2.16 kg and MFR₂₁ denotes the measurementhas been carried out under a load of 21.6 kg, respectively.

FRR

Flow Rate Ratio (FRR) is a ratio of two melt flow rates, measured underdifferent loads. The loads are denoted in the subscript. Thus,FRR_(21/2) denotes the ratio of MFR₂₁ to MFR₂.

SHI

Shear Thinning Index (SHI) of polymers has been determined usingRheometrics RDA II Dynamic Rheometer. The measurements have been carriedout at 190° C. temperature under nitrogen atmosphere. The measurementsgive storage modulus (G′) and loss modulus (G″) together with absolutevalue of complex viscosity (η*) as a function of frequency (ω) orabsolute value of complex modulus (G*).η*={square root}(G′ ² +G″ ²)/ωG*=(G′ ² +G″ ²)

According to Cox-Merz rule complex viscosity function, η*(ω) is the sameas conventional viscosity function (viscosity as a function of shearrate), if frequency is taken in radis. If this empiric equation isvalid, then absolute value of complex modulus corresponds shear stressin conventional (that is stedy state) viscosity measurements. This meansthat the function η*(ω) is the same as viscosity as a function of shearstress.

In the present method viscosity at a low shear stress or η* at a low G*(which serve as an approximation of so called zero viscosity) is used asa measure of average molecular weight. On the other hand, shearthinning, that is the decrease of viscosity with G*, gets morepronounced the broader is molecular weight distribution. The propertycan be approximated by defining a so called shear thinning index, SHI,as a ratio of viscosities at two different shear stresses. In theexamples below the shear stress (or G*) 0 and 100 kPa have been used.Thus:SHI _(0/100)=η*₀/η*₁₀₀where

-   -   η*₀ is the zero shear rate viscosity    -   η*₁₀₀ is the complex viscosity at G*=100 kPa.

As mentioned above storage modulus function, , G′(ω), and loss modulusfunction G″(ω), are obtained as primary functions from dynamicmeasurements. The value of the storage modulus at a specific value ofloss modulus increase with broadness of molecular weight distribution.However this quantity is highly dependent on the shape of molecularweight distribution of the polymer. In the examples the value of G′ atG″=5 kPa is used.

Density

Density was measured from compression moulded specimen at 23° C. in awater bath according to an ultrasound measurement method using Tecrad DS500 equipment. The method was calibrated with samples having a densitydeterminded according to ISO 1183.

Dart Drop

Dart drop was measured from film samples using the ISO 7765-1 method.

Gel Rating

The gel rating was observed visually from film samples. The samples wererated from −− (having a lot of gels) to ++ (having no or only a smallnumber of gels).

Gloss

Gloss was measured according to ASTM D 2457v.

Haze

Haze was measured according to ASTM 1003.

Puncture

The puncture test was performed as follows. The film was mechanicallyclamped allowing circular testing area of diameter 50 mm. The film wasthen punctured by a striker (diameter 20 mm). The force and travel tothe puncturing point were measured and the required energy wascalculated. Travelling speed of the striker was 200 mm/min.

Molecular Weight

The molecular weight distribution is measured by using the sizeexclusion chromatography (SEC). In the examples this was done by using aWaters 150 CV plus no. 1115. A refractive index (RI) detector and aviscosity detector were used. The instrument was calibrated with anarrow molecular weight distribution polystyrene sample. The columnswere 3 HT6E styragel from Waters at an oven temperature of 140° C.

EXAMPLE 1

Into a 50 dm³ loop reactor, operated at 70° C. temperature and 45 barpressure, were continuously fed isobutane diluent, ethylene, 1-hexenecomonomer, hydrogen, and a Ziegler-Natta Type polymerization catalyst(prepared according to example 3 of EP-A1-0 688 794) so that about 1.5kg/h of polymer was formed.

The slurry was withdrawn from the reactor and introduced into another,500 dm³ loop reactor, operated at 80° C. temperature and 42 barpressure, where additional isobutane, ethylene, 1-hexene and hydrogenwere added, so that 32 kg/h of polymer having MFR₂ of 310 g/10 min and adensity of 949 kg/m³ was withdrawn from the reactor.

The polymer slurry was led into a flash tank, where the hydrocarbonswere removed from the polymer. The polymer was then introduced into afluidized bed gas phase reactor, where additional ethylene and hydrogentogether with 1-butene comonomer were introduced.

From the gas phase reactor polymer was withdrawn at a rate of 81 kg/h.The powder was mixed with additives (Ca-stearate, antioxidant andprocess stabilizer) and compounded in a counterrotating twin screwextruder (JSW C1M90P extruder). The pelletized polymer had an MFR₂₁ of27 g/10 min and a density of 923 kg/m³.

COMPARATIVE EXAMPLE 1

The process of example 1 was repeated, except that 1-butene was used asa comonomer in the loop reactor instead of 1-hexene and propane was usedas a diluent instead of isobutane. The data is shown in Table 1.

EXAMPLES 2 TO 4

The process of Example 1 was repeated with slightly different processconditions. The material property can be found in Table 1. TABLE 1Properties of the polymers of Examples 1 to 4. Example 1 2 3 4 C.E.1Loop MFR₂ (g/10 min.) 310 550 320 300 300 Loop density (kg/m³) 949 941954 949 950 Split (% in GPR) 59 59 58 59 59 MFR₂₁ (g/10 min.) 27 33 2926 23 FRR_(21/2) 27 24 22 24 25 SHI(5/300) 40 29 33 34 30 Density(kg/m³) 923 922 923 923 922

EXAMPLE 5

The materials of the Examples 1 to 4 and Comparative to Example 1 wereblown to a film of 25 μm thickness an a Collin film line, with a diediameter of 30 mm, a die gap of 0.75 mm, a BUR (blow-up ratio) of 3.2and a frost line height of 160 mm. The results are shown in Table 2.They are referred to as Type 1 film materials. TABLE 2 Type 1 filmproperties for a film prepared on an Collin laboratory line Polymer ofExample 1 2 3 4 C.E.1 Gels −−/−/0/+/++ (+)+ ++ ++ ++ ++ Dart drop(g) >1700 >1700 >1700 >1700 1040 Puncture resist. energy (J) 2.7 2.7 2.82.2 N.M Puncture resist. force (N) 40 38 41 37 N.M Haze 84 79 82 84 N.MGloss 9 10 9 9 N.MN.M. denotes for not measured

EXAMPLES 6 TO 7

The process of Example 1 was repeated except that 1-butene was used as acomonomer and propane as a diluent in the loop reactor and a mixture of1-butene and 1-hexene was used as comonomers in a gas phase reactor. Theprocess conditions were set to obtain materials according to Table 3.

COMPARATIVE EXAMPLES 2 TO 3

The process of Comparative Example 1 was repeated except that theprocess conditions were set to produce the polymers according to Table3. TABLE 3 Properties of the polymers of Examples 6 to 7 and ComparativeExamples 2 to 3 Example 6 7 C.E.2 C.E.3 Loop MFR₂ (g/10 min.) 6 3 7 8Loop density (kg/m³) 935 934 935 936 Split (% in GPR) 39 41 41 40 Ratioof 1-butene to 1-hexene (mol/mol) 0.11 0.19 ∞ ∞ MFR₂₁ (g/10 min.) 48 3747 45 FRR_(21/2) 32 38 43 42 Density (kg/m³) 925 924 923 922

EXAMPLE 8

The procedure of Example 5 was repeated except that the film thicknesswas 25 μm, die diameter 60 mm, die gap 1.5 mm, BUR (blow-up ratio) 2 andfrost line height 120 mm, and that the materials of Examples 6 to 7 andComparative Examples 2 to 3 were used. The data is shown in Table 4.These are referred to as Type 2 film materials. TABLE 4 Type 2 filmproperties an Collin laboratory line Polymer of Example 6 7 C.E.2 C.E.3Gels - −/−/0/+/++ + ++ (+)+ (+)+ Dart drop (g) 63 84 45 41 Punctureresist. energy (J) 3.6 4.7 3.0 3.1 Puncture resist. force (N) 51 59 4141 Haze 15 15 16 16 Gloss 74 75 72 74

EXAMPLE 9

Into a 50 dm³ loop reactor, operated at 70° C. temperature and 65 barpressure, were continuously fed propane diluent, ethylene, hydrogen andZiegler-Natta type polymerization catalyst (prepared according toExample 3 of EP-A-688794), so that about 1.5 kg/h of polymer was formed.

The slurry was withdrawn from the reactor and introduced into another,500 dm³ loop reactor, operated at 95° C. temperature and 60 barpressure, where additional propane, ethylene and hydrogen were added, sothat 32 kg/h of ethylene homopolymer having MFR₂ of 450 g/10 min anddensity of 975 kg/m³ was withdrawn from the reactor.

The polymer slurry was led into a flash tank where the hydrocarbons wereremoved from the polymer. The polymer was then introduced into afluidized bed gas phase reactor, operated at 75° C. temperature and 20bar pressure, where additional ethylene and hydrogen, together with1-butene and 1-hexene comonomers, were introduced. From the gas phasereactor polymer was withdrawn at a rate of 80 kg/h. The powder was mixedwith additives (Castearate, antioxidant and process stabilizer) andcompounded in a counterrotating twin screw extruder JSW CIM90P extruder.The palletized polymer had an MFR₂₁ of 7.5 g/10 min and density of 944kg/m³.

The data can be found in table 5.

COMPARATIVE EXAMPLE 4

The process of Example 9 was repeated except that only 1-butene was usedas a comonomer in the gas phase reactor. The data can be found in Table5. TABLE 5 Properties of the polymers of Example 9 and ComparativeExample 4 Example 8 C.E.4 Loop MFR2 (g/10 min) 450 660 Loop density(kg/m³) 975 975 Split (% in GPR) 60 60 MFR₂₁ (g/10 min) 7.5 5.5FRR_(21/5) N.M. 21 SHI (5/300) 67 70 Density (kg/m³) 944 945N.M. denotes fro not measured

EXAMPLE 10

The polymers of Example 9 and Comparative Example 4 were blown to filmsby using the equipment and procedure described in Example 5. The data isshown in Table 6. TABLE 6 Type 1 film properties on Collin laboratoryline Polymer of Example 8 C.E.4 Gels −−/−/0/+/++ — — Dart drop (g) 308279 Tear resistance MD (N) 0.08 0.08 Tear resistance TD (N) 2.6 2.6

1. Film with a high impact strength characterized in that the filmconsists of a bimodal terpolymer comprising a) a low molecular weighthomopolymer of ethylene and b) a high molecular weight terpolymer ofethylene, 1-butene and a C₆ to C₁₂ α-olefin.
 2. Film with a high impactstrength characterized in that the film consists of a bimodal terpolymercomprising a) a low molecular weight polymer which is a binary copolymerof ethylene and a C₄ to a C₁₂ α-olefin and b) a high molecular weightpolymer which is either a binary copolymer of ethylene and 1-butene, ifthe low-molecular weight polymer of a) is a binary copolymer of ethyleneand a C₆ to C₁₂ α-olefin, or a terpolymer of ethylene, 1-butene and a C₆to a C₁₂ α-olefin.
 3. A film according to claim 1, characterized in thatthe film if extruded on a Collin film line into a thickness of 25 μm,with a die diameter of 30 mm, a die gap of 0.75 mm, a BUR (blow-upratio) of 3.2 and a frost line height of 160 mm, has a dart-drop valueof at least 180 g.
 4. A film according to claim 2, characterized in thatthe film if extruded on a Collin film line into a thickness of 25 μm,with a die diameter of 60 mm, die gap of 1.5 mm, a BUR (blow-up ratio)of 2 and a frost line height of 120 mm, has a dart-drop value of atleast 50 g.
 5. A film according to claim 1, characterized in that thefilm if extruded on a Collin film line into a thickness of 25 μm, with adie diameter of 30 mm, a die gap of 0.75 mm, a BUR (blow-up ratio) of3.2 and a frost line height of 160 mm, has a dart-drop value of at least1500 g.
 6. A film according to claim 1, characterized in that the C₄ toC₁₂ α-olefin of the low molecular weight copolymer fraction is selectedfrom the group of 1-butene, 1-hexene, 4 methyl-1-pentede, 1-octene and1-decene.
 7. A film according to claim 1, characterized in that the C₆to C₁₂ α-olefin of the high molecular weight copolymer fraction isselected from the group of 1-hexene, 4 methyl-1-pentene, 1-octene and1-decene.
 8. A film according to claim 4, characterized in that the filmhas a haze value equal or lower than 20 and a gloss value of at least60.
 9. A film according to claim 1, characterized in that the bimodalterpolymer has a weight average molecular weight of 190,000 to 400,000g/mol.
 10. A film according to claim 1, characterized in that thebimodal terpolymer has a weight average molecular weight of 240,000 to500,000 g/mol.
 11. A film according to claim 2, characterized in thatthe bimodal terpolymer has a weight average molecular weight of 110,000to 210,000 g/mol.
 12. A film according to claim 1, characterized in thatthe low molecular weight copolymer fraction has a weight averagemolecular weight of 4,500 to 55,000 g/mol and the high molecular weightcopolymer fraction has a weight average molecular weight of 450,000 to1,000,000 g/mol.
 13. A film according to claim 2, characterized in thatthe low molecular weight copolymer fraction has a weight averagemolecular weight of 25,000 to 110,000 g/mol and the high molecularweight copolymer fraction has a weight average molecular weight of100,000 to 400,000 g/mol.
 14. A film according to claim 1, characterizedin that the bimodal terpolymer has a melt flow rate MFR₂₁ of 7 to 40g/10 min.
 15. A film according to claim 1, characterized in that thebimodal terpolymer has a melt flow rate MFR₂₁ of 2 to 25 g/10 min.
 16. Afilm according to claim 2, characterized in that the bimodal terpolymerhas a melt flow rate MFR₂₁ of 15 to 80 g/10 min.
 17. A film according toclaim 1, characterized in that the low molecular weight copolymerfraction has a melt index MFR₂ of 200 to 800 g/10 min.
 18. A filmaccording to claim 1, characterized in that the low molecular weightcopolymer fraction has a melt index MFR₂ of 300 to 1200 g/10 min.
 19. Afilm according to characterized in that the low molecular weightcopolymer fraction has a melt index MFR₂ of 1 to 50 g/10 min.
 20. A filmaccording to claim 1, characterized in that the bimodal terpolymer has adensity of 910 to 950 kg/m³.
 21. A film according to claim 1,characterized in that the bimodal terpolymer has a density of 935 to 970kg/m³.
 22. A film according to claim 2 and 19, characterized in that thebimodal terpolymer has a density of 900 to 935 kg/m³.
 23. A filmaccording to claim 1, characterized in that the low molecular weightcopolymer fraction has a density of 940 to 980 kg/m³.
 24. A filmaccording to claim 1, characterized in that-the low molecularweight-copolymer fraction has a density of 970 to 980 kg/m³.
 25. A filmaccording to claim 2, characterized in that the low molecular weightcopolymer fraction has a density of 925 to 950 kg/m³.
 26. A filmaccording to claim 1 characterized in that the low molecular weightcopolymer fraction constitutes of 30 to 60% by weight of the totalcomposition.
 27. A film according claim 1, characterized in that thecomonomer content in the high molecular weight copolymer fraction is 2.5to 11.0% per mol.
 28. A film according to claim 1, characterized in thatthe comonomer content in the high molecular weight copolymer fraction is0.5% to 3.5% per mol.
 29. A film according to claim 2, characterized inthat the comonomer content in the high molecular weight copolymerfraction is 3.5 to 10.5% per mol.
 30. A process for producing a filmwith a high impact strength according to any of the preceding claimswhereby the process is a multi-stage process comprising a first reactionstep wherein the low molecular weight polymer is produced and a secondreaction step where the high molecular weight copolymer is producedcharacterized in that the first reaction step takes place in a slurryreactor whereby the ethylene or the ethylene and the C₄ to C₁₂ α-olefinare polymerized in an inert low boiling hydrocarbon medium in thepresence of a catalyst and a chain transfer agent such as hydrogen andsubsequently, the slurry is removed from the loop reactor andtransferred to a separation unit where the hydrocarbons including theeventually used C₄to C₁₂α-olefin copolymers and the chain transfer agentare separate from the polymer and subsequently, the polymer containingthe active catalyst is introduced into the gas phase reactor where thepolymerization proceeds in the presence of additional ethylene, 1-buteneand optional C₆to C₁₂ α-olefin and optionally chain transfer agent toproduce the high molecular weight polymer.
 31. A process according toclaim 30 characterized in that the slurry reactor is a loop reactor. 32.A process according to claim 30 characterized in that the catalyst is aZiegler-Natta or a single-site catalyst.
 33. A process according toclaim 30 characterized in that the inert low boiling hydrocarbon mediumis isobutene or propane.
 34. A process according to claim 30characterized in that the molar ratio of hydrogen to ethylene is between0.1 and 1.0 mol/mol for producing the low molecular weight polymer. 35.A process according to claim 30 characterized in that the temperature inthe gas phase reactor is between 70 to 100° C.
 36. A process accordingto claim 30 characterized in that the pressure in the gas phase reactoris between 10 to 40 bar.
 37. A process according to claim 30characterized in that the molar ratio between hydrogen and ethylene isfrom 0.001 to 0.1 mol/mol.
 38. A process according to claim 30characterized in that the molar ration is the α-olefin is from 0.05 to0.5 mol/mol.
 39. A film according to claim 1 produced by a processaccording to claim 30.